Tire Pressure Light On

That's normal. You lose about 1 PSI for every 10°F degrees.

Also, air naturally leaks out over time, causing even lower PSI. Something you typically will not noticed, since tires hold their shape so well nowadays.

As for driving with pressure the dealer set, that's asking for trouble. They barely set to minimum in the first place.

If you haven't checked (cold measure) in awhile and the warning is on, you're dangerously low. That's 25% below the automaker recommendation, a known compromise by federal safety standards.
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Jangell2,

Since the warning indicator is on, use a accurate Tire Pressure Guage and check all 4 tires. You will find which one is low.

I had it happen to me once as well. But, could not see the tire that was low as well, but when I used a good digital guage I found the tire easily and it was at 22 PSI and should have been at 32 PSI.

I believe the TPMS system will alert once there is about a 6-8 PSI drop from set pressures.

Once you have added the correct amount of air to match the placard on your driver door jamb, your light should go out soon thereafter.

Hope that helps.
Bob

 

Let us know how you make out.

For anyone following this thread, who wants to know a bit more on how the system works, Toyota has a bulletin on initializing the TPMS. I'll post a link below, but if the link gets "broken," the TSB is numbered T-SB-0151-09, and applies to several Toyota models. See also T-SB-0345-08, regarding cold-weather.


http://priustouringclub.net/librairie/mediatheque/pdf/Prius3_2010_owner_manual/Maintenance%20and%20Care/Tire%20Pressure%20Warning%20System%20Activation%20and%20Initialization.pdf

 

Believe the light - TPMS works. One (or more) of your tires is now more than 8lbs below the "set point".

The set point is whatever the pressure was when the system was initialized - and if the dealer set it at 35lbs front / 33lbs rear, that means one of your tires is under 27lbs or possibly even under 25lbs.

It's possible that the system was initialized with a warm tire - i.e: WRONG - and now that cold weather has hit (and your tires are cooling down), the cold tire pressure is that low.

 

Measuring the pressure with cold tires removes some of the variability. Hot tires will run a few psi higher, but there is no way to know exactly how much higher they should be. Filling them hot is better than not filling them at all, but to be accurate, recheck the pressure later when the tires have cooled.

Tom

 

Advance Auto Parts has a cheap, small inflator on sale. It is pretty small...about 8 inches square and less than two iinches thick. It is ordinarily about $16 and is still shown at that price but it rings up at $9.88 or thereabouts which is the price shown on the current flyer. Works fine. The built in gauge stinks, but it will pump up to more than we need even for the compact spare.

It may not be the fanciest or most quality inflator but it works and it is small. What else do you need? Yeah, I know...nothing but the best for my sweetums. I also use a $2 slide air gauge that is short so it fits inside the gas tank cover so it is always available and when it breaks, it breaks.

 

Sears has a good, cheap gauge, too. If you can get a GH Meiser gauge, you're doing well, though they're all made in China nowadays...

This saga is a great reason to invest in an air compressor for home, if you need an excuse w/ your significant other!

 

You might consider one of the combination units that have a booster battery and an inflater. They can be a lifesaver if you ever accidentally discharge your 12V battery by leaving a light on, or the hatch open.

Tom

 

That unit is probably overkill for your needs. Check out Tom's (qbee) suggestion, and look for a combination battery jumper/tire inflator.

 

I think the digital gauges are just analog gauges with a digital readout. I buy good quality analog gauges, no batteries, and they seem to do just fine, + or - 1 pound is close enough.

Check some of the threads here on tire pressure, you might find you want to use higher than the Toyota recommended pressures.

 

Warm tire reading 35lbs is a cold tire reading of 32lbs or less... Your rears look fine but the fronts likely need more air.

 

There are many pressure sensing ICs available. Generally digital pressure gauges use IC pressure transducers, as they are cheaper than building from scratch. Accuracy can vary from garden variety crappy to astonishingly accurate, depending on what you are willing to pay.

Tom

 

Is this ^ done by the dealer or am I supposed to? I had a 600+ mile roadtrip this weekend and in the beginning of the trip the TP light did the blink then solid thing which indicates a malfunction in the system. It did it once more a few minutes later then nothing the rest of the way or the return. Checked my pressure, all was good. Should I take it in or did it correct itself?? Thanks.

 

As indicated in the TSB the dealer needs to activate the sensors during PDS. Then they also initialize the system.

The initialization also need to be done by the owner any time they change tire pressure.

If you've had no issues until now, my guess is the dealer did the activation & initialization during PDS, and now you may have a system issue.

 

If it is not malfunctioning it will not do any good to take it in. They will just check the tires, reset it, and tell you it's OK. You have already done that.

You may well have an intermittent failure but if it's not broke when they look at it they will do nothing. If it is a malfunction it will probably break again and maybe it will stay broken so you can have it fixed, but the important thing is your tire pressures are OK, just check them often.